Ordinarily, the ventilating-power of ventilators has been investigated only for the horizontal winds, but the wind does not always blow in this direction only but blows in all directions. Accordingly, it is desired to test the ventilator for winds of all directions, for otherwise we can not judge rightly the capacities of the ventilator. When we take the origin point 0 in the centre of a ventilator and draw a short line pararell to the wind blowing to the ventilator, taking the length of the line proportionally to the ventilating power of the ventilator, the length of the short line will give the ventilating power of the ventilator for that wind direction. If we draw such lines for the winds of all directions, the outer ends of the short lines will form a closed solid surface. This is the ventilating-power-solid of the ventilator. This power-solid has a special form and size for each ventilator, and represents the whole phase of its ventilating power. But because it is difficult either to show in drawing the power-solid or to measure it, we will cut this solid by the planes XY, XZ and YZ, passing the origin 0 and perpendicular to one another, and show the circumference curves of the sections. These are the ventilating-power-curves of the ventilator. If we draw a number of concentric circles about the origin 0 as the centre, by these as scales we can read directly the ventilating power for any arbitrary direction of the wind. By the ventilating-power-curves we can understand clearly the capacity of a ventilator, and we can judge distinctly the relative power of the ventilators. This report concerns the ventilating-power-curves of nine ventilators on the market, eight standard types of the ventilator and eighteen various trial manufactures-thirty-five samples all-that were tested. In the test, the wind velocity of 2m/sec was used, and the curves were drawn of the velocities of the air current through the duct prepared for this examination. Therefore, these curves show not the actual ventilating power but its relative magnitude, and will be sufficient for comparing the capacities of the ventilators. From the curves given in this report, we know that no ventilator on the market has satisfactory ventilating qualities, while we notice many good qualities in the standard types, especially in H-type. The trial manufactures were prepared by studying the standard types and by combining their strong points, and among them are some samples of very good ventilating capacity. Above all, sample No. 36, a combination of two H-types on the same level at right angles to each other, shows nearly an ideal shape and size of the ventilating-power-curve.
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